1. Technical Field
Example embodiments of the present invention relate in general to wireless communication technologies and more specifically to a wireless channel access method which may improve a connection speed via wireless channel and reduce power consumption and an apparatus for performing the method.
2. Related Art
With the development of information communication technologies, a variety of wireless communication technologies have been developed. Among these technologies, wireless local area network (WLAN) technology makes wireless connection to the Internet possible at homes or businesses or in specific service providing areas using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), or the like, based on wireless communication technologies.
The standard of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard has been developed as a standard for WLAN technology.
IEEE 802.11a provides a transmission speed of 54 Mbps using an unlicensed band at 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps by applying a direct sequence spread spectrum (DSSS) method at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps by applying orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps when using two spatial streams and a bandwidth of 40 MHz, and provides a transmission speed of 600 Mbps when using four spatial streams and a bandwidth of 40 MHz.
As such WLAN technology becomes more prevalent and its applications become more diverse, there is increasing demand for new WLAN technology that can support a higher processing throughput than a data processing speed supported by IEEE 802.11n.
Very high throughput (VHT) WLAN technology is one among IEEE 802.11 WLAN technologies proposed to support a data processing speed of 1 Gbps or higher. Among these, IEEE 802.11ac has been developed as a standard for providing VHT in a band at 5 GHz, and IEEE 802.11ad has been developed as a standard for providing VHT in a band at 60 GHz.
Meanwhile, a system based on such WLAN technology may adopt carrier sense multiple access/collision avoidance (CSMA/CA) as a wireless channel access method.
In order for a WLAN terminal to connect to an access point, the WLAN terminal first determines whether a wireless channel is already occupied by another terminal, waits for a predetermined time period when the wireless terminal is determined to be in an idle state, and then transmits an authentication frame to the access point, thereby starting to perform a connection process.
In such a connection process, when a small number of terminals carry out channel access in order to simultaneously connect to the access point, data may be transmitted to the access point within a time range of a small contention window (CW).
However, when thousands of terminals simultaneously attempt to connect to the access point such as in a smart grid or a sensor network, a probability of a plurality of terminals simultaneously transmitting data is dramatically increased.
Accordingly, there is a problem that a corresponding terminal has to wait for completion of data transmission of a large number of other terminals having a shorter back-off timer than a back-off timer of the corresponding terminal before starting first data transmission.
In addition, when transmitting data after expiration of the back-off timer, the terminal has a significantly high possibility of occurrence of collision with data transmitted by other neighboring terminals which are in a hidden-node relationship, and therefore the CW has to be increased and the data has to be retransmitted.
Furthermore, since an opposite-side terminal in which data collision occurs as well as the terminal itself should also carry out data retransmission, the number of data retransmissions of terminals within a basic service set (BSS) is also rapidly increased, thereby causing intense wireless channel access competition.